1. Field of the Invention
The present invention relates to rigid or plasticized, stabilized thermoplastic molding compositions based on halogen-containing polymers, in particular polyvinyl chloride or polymers containing essentially vinyl chloride.
2. Discussion of the Background
It is known that chloride-containing polymers are readily degraded by the action of heat, for example during processing. This degradation leads to undesired discolorations and to an impairment of the mechanical properties. Consequently, this degradation is avoided by adding stabilizers to the polymers before processing. In the case of polyvinyl chloride and copolymers containing essentially vinyl chloride, particular use is made of organotin compounds, inorganic and organic lead salts, organic antimony compounds or combinations of cadmium carboxylates and barium carboxylates and also of a mixture of zinc soaps and polyoxazolines. These so-called primary stabilizers are frequently supplemented with costabilizers to improve their effectiveness. The modes of action of primary or costabilizers and their combined action (synergism) are described in the relevant literature, for example in the publication by L. I. Nass, "Heat Stabilizers", Kirk-Othmer Encyclopedia of Chemical Technology, volume 12, 3rd edition, page 225, published by John Wiley and Sons, 1980.
Essentially, these are costabilizers which improve the initial color and the ultimate stability of the chlorine-containing polymer. For instance, epoxy compounds, polyols, organic phosphites, substituted dihydropyridines, 1,3-diketones or combinations of these compounds are used.
At the present time, there are no highly effective costabilizers for primary stabilizers based on polymers. Therefore, there remains a need for substances or mixtures of substances which enhance or reinforce the heat-stabilizing action of polymeric primary stabilizers.